The objectives of this project continue to be the study of the relation between conformational changes in enzymes and the catalytic efficiency of their action. We are studying proteinases (pepsin, papain, thermolysin) from this point of view by using peptide substrates and inhibitors whose structure has been varied systematically, and also have attached groups that act as fluorescent probes for hydrophobic interaction. Fluorescence studies are also being conducted on changes in the intrinsic fluorescence of active site tryptophan residues of these enzymes upon the binding of peptide substrates and inhibitors. BIBLIOGRAPHIC REFERENCES: The mechanism of the catalytic action of pepsin and related acid proteinases. J.S. Fruton. Advan. Enzymol. 44 (in press), 1976. Kinetics of the action of papain on fluorescent peptide substrates. J.A. Mattis and J.S. Fruton. Biochemistry (in press), 1976.